Testing & modern typing
pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.
Capture stdout and stderr with pytest capsys
Use pytest's capsys fixture to capture and assert on standard output and error streams in your tests.
import pytest
# Function under test
def greet(name):
print(f"Hello, {name}!")
print(f"Error: {name} not found", file=sys.stderr)
def test_captures_stdout_and_stderr(capsys):
greet("Alice")
captured = capsys.readouterr()
assert "Hello, Alice!" in captured.out
assert "Error: Alice not foun…How to Mock pathlib Path.read_text with mock_open in Python
Mock pathlib.Path.read_text using patch and mock_open to test file-reading code without touching the filesystem.
import pathlib
from unittest.mock import mock_open, patch
def read_config(filepath: pathlib.Path) -> str:
"""Read file content with pathlib."""
return filepath.read_text()
if __name__ == "__main__":
mock_data = "version: 1.0\nname: demo-app"
with patch("pathlib.Path.open", mock_open(read_data=mo…Browse by section
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Testing & modern typing — Python code examples
What you will find here
This page collects testing & modern typing snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
Samples vs tutorials and challenges
Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.